1. Field of the Invention
The present invention relates to a processor for extracting ocean bottom properties in real-time. More particularly, the invention relates to a method for the extraction of the bottom loss and the bottom scattering strength coefficient in real-time.
2. Description of the Prior Art
In bottom limited environments, sonar signals must bounce off the bottom and the surface several times in order to increase the detection range and the performance of the sonar system. As is known in the art, sonar performance and detection range are often estimated or predicted by computing active signal excess. Active signal excess, by definition, is the received signal to noise ratio divided by the signal to noise ratio required for detection, for a given probability of false alarm and detection. The results of the active signal excess calculations are then used to select the optimum mode for the sonar system including best current mode, pulse length, and range scale settings. However, to accurately predict the range at which a return signal can be detected as well as sonar performance, one must be able to accurately predict the amount of attenuation of the sonar signal due to the absorption of sound by the bottom as well as the reflection of sound by the bottom. Over estimating or under estimating the amount of bottom loss or bottom scattering greatly affects the calculation of active signal excess. Thus, to optimize the active signal excess performance prediction in bottom limited environments, it is necessary to accurately predict the bottom loss and the bottom scattering coefficient. Additionally, accurately determining bottom loss and bottom scattering coefficient enables one to distinguish and differentiate bottom types.
Current methods for determining values for the bottom loss and the bottom scattering coefficient suffer from one or more disadvantages or defects which limit their application for many uses. For example, one method for determining bottom loss relies on estimates for bottom loss and bottom scattering obtained by surveying the areas of the bottom, obtaining bottom samples (sediment cores) or obtaining extensive sonar data and accurately measuring values for the bottom loss and bottom scattering using the sediment cores or the extensive sonar data. However, such a method requires that large areas of the bottom be surveyed, often requiring a large amount of time, and cannot be performed in situ or in real-time. Additionally, in many shallow bottom limited areas, currents, biologics or human activities can change the thickness and make-up of the bottom materially affecting the bottom loss.
Other methods, such as that described in U.S. Pat. No. 3,555,499, determine a single value for attenuation due to the ocean bottom by comparing magnitude of transmitted sonar signals with the magnitude of the returns. However, such methods do not generate independent values for the bottom loss and the bottom scattering coefficient nor do such methods compute bottom attenuation as a function of grazing angle. Additionally, the method of 3,555,499 does not consider environmental parameters affecting depth and absorption measurements such as the sound speed profile. There is no method for the real-time determination of values for bottom loss and bottom scattering coefficient needed to accurately predict sonar performance. Such a method would be a welcome addition to the art.